US 20070147521 A1 Abstract A MIMO communication system implements an interleaver design with multiple encoders for more than two transmit antennas for high throughput WLAN communication systems. Multiple encoders are utilized in the transmitter and multiple decoders are utilized in the receiver, wherein each encoder operates at lower clock speed than would be necessary with a single encoder. In conjunction with using multiple encoders, a modified interleaving function for each spatial stream processing allows fully exploring the diversity gains. The provided interleaving function is suitable for transmitter architectures with multiple encoders. Similarly, a modified de-interleaving function is provided that is suitable for receiver architectures with multiple decoders.
Claims(16) 1. A method of data communication in a wireless system, comprising the steps of:
parsing a bit stream into multiple spatial data streams; encoding the multiple spatial data streams via multiple encoders, wherein each spatial data stream is encoded by a corresponding encoder to generate an encoded stream; interleaving the bits in all encoded streams and performing bit circulation to increase diversity of the wireless system; and transmitting the bits of each spatial data stream. 2. The method of further parsing each encoded stream into a plurality of encoded spatial data streams; interleaving the bits in all encoded spatial data streams and performing bit circulation to increase diversity of the wireless system. 3. The method of 4. The method of splitting the bits in each stream into multiple groups corresponding to subcarriers in a transmission symbol; circulating the bits among the groups; and combining the bits from the different data streams to form a new bit sequence for transmission. 5. The method of splitting the bits in each data stream into multiple groups corresponding to subcarriers in a transmission symbol; circulating the bits among the groups; and combining the bits for the different data streams to form a new bit sequence for transmission. 6. The method of 7. The method of 8. The method of 9. A wireless communication system, comprising:
a transmitter including:
a parser for parsing a bit stream into multiple spatial data streams;
an encoder for encoding the multiple spatial data streams via multiple encoders, wherein each spatial data stream is encoded by a corresponding encoder to generate an encoded stream;
an interleaver for interleaving the bits in all encoded streams and performing bit circulation to increase diversity of the wireless system; and
wherein the transmitter transmitting the bits of each spatial data stream.
10. The system of the parser further parses each encoded stream into a plurality of encoded spatial data streams; and the interleaver further interleaves the bits in all encoded spatial data streams and performs bit circulation to increase diversity of the wireless system. 11. The system of 12. The system of 13. The system of 14. The system of 15. The system of 16. The system of splitting the bits in each stream into multiple groups corresponding to subcarriers in a transmission symbol; circulating the bits among the groups; and combining the bits from the different data streams to form a new bit sequence for transmission. Description The present invention relates generally to data communication, and more particularly, to data communication with transmission diversity using Orthogonal Frequency Division Multiplexing (OFDM) in multiple antenna channels. In wireless communication systems, antenna diversity plays an important role in increasing the system link robustness. OFDM is used as a modulation technique for transmitting digital data using radio frequency signals (RF). In OFDM, a radio signal is divided into multiple sub-signals that are transmitted simultaneously at different frequencies to a receiver. Each sub-signal travels within its own unique frequency range (sub-channel), which is modulated by the data. OFDM distributes the data over multiple channels, spaced apart at different frequencies. OFDM modulation is typically performed using a transform such as Fast Fourier Transform (FFT) process wherein bits of data are encoded by an encoder in the frequency-domain onto sub-channels. As such, in the transmitter, an Inverse FFT (IFFT) is performed on the set of frequency channels to generate a time-domain OFDM symbol for transmission over a communication channel. The IFFT process converts the frequency-domain phase and amplitude data for each sub-channel into a block of time-domain samples which are converted to an analogue modulating signal for an RF modulator. In the receiver, the OFDM signals are processed by performing an FFT process on each symbol to convert the time-domain data into frequency-domain data, and the data is then decoded by a decoder by examining the phase and amplitude of the sub-channels. Therefore, at the receiver the reverse process of the transmitter is implemented. Further, transmit antenna diversity schemes are used to improve the OFDM system reliability. Such transmit diversity schemes in OFDM systems are encoded in the frequency-domain as described. With the increase in transmission rates, higher operational speeds in the encoder and decoder are resulting in difficulties in implementing such channel encoders/decoders. The transmitter architecture with only one encoder is adopted in current IEEE 802.11n (high throughput WLAN) proposals. The interleaver design in the high throughput wireless local area network (WLAN) systems is an important issue for MIMO-OFDM transmission. In the current approaches in IEEE 802.11n standards (S.A. Mujtaba, “TGn Sync Proposal Technical Specification,” a contribution to IEEE 802.11, 11-04/0889r4, March 2005, and C. Kose and B. Edwards, “WWiSE Proposal: High throughput extension to the 802.11 Standard,” a contribution to IEEE 802.11, 11-05-0149r2, March 2005, incorporated herein by reference), the transmitter architecture with single channel encoder is considered regardless of the number of the transmit antennas. When the data rate or the number of the data streams increases, the encoder/decoder must operate with very high speed, causing circuit design and timing implementation difficulties. According to an embodiment of the present invention a solution to overcoming the aforementioned implementation difficulties for high rate transmissions is to utilize multiple encoders in the transmitter, and thus multiple decoders at the receiver, wherein each encoder operates at lower clock speed than would be necessary with a single encoder. In conjunction with using multiple encoders, a modified interleaving function for each spatial stream processing allows fully exploring the diversity gains. The provided interleaving function is suitable for transmitter architectures with multiple encoders. Similarly, a modified de-interleaving function is provided that is suitable for receiver architectures with multiple decoders. Accordingly, in one implementation, the present invention provides a method of data communication in a wireless system, comprising the steps of: parsing a bit stream into multiple spatial data streams; encoding the multiple spatial data streams via multiple encoders, wherein each spatial data stream is encoded by a corresponding encoder to generate an encoded stream; interleaving the bits in all encoded streams by performing bit circulation to increase diversity of the wireless system; and transmitting the bits of each spatial data stream. An additional step includes further parsing each encoded stream into a plurality of encoded spatial data streams, wherein the steps of interleaving further includes the steps of interleaving the bits in all encoded spatial data streams by performing bit circulation to increase diversity of the wireless system. The present invention further includes a wireless communication system that implements the method of the present invention. These and other features, aspects and advantages of the present invention will become understood with reference to the following description, appended claims and accompanying figures. According to an embodiment of the present invention a solution to overcoming the aforementioned implementation difficulties for high rate transmissions is to utilize multiple encoders in the transmitter, and thus multiple decoders at the receiver, wherein each encoder operates at lower clock speed. In conjunction with using multiple encoders, the interleaving function for each spatial stream processing path is modified according to the present invention to fully explore the diversity gains. The present invention provides modified interleaving functions suitable for transmitter architectures with multiple encoders. Similarly, the present invention provides modified de-interleaving functions suitable for receiver architectures with multiple decoders. An implementation of a modified interleaving function according to the present invention includes two stages of operations: frequency interleaving, and bit circulation. The receiver In the transmitter Three stages of operations are involved with interleaver operation: (1) first permutation operations by first permutation functions For each spatial stream processed within the interleaver However, for the third operation (i.e., frequency rotations), the amount of frequency rotation by the frequency rotation units The bit circulation operations can be an extension of an interleaver design in said commonly assigned patent application Ser. No. 11/253,855, filed Oct. 18, 2005, entitled “A method of designing interleavers for multiple-encoder MIMO OFDM systems” (incorporated herein by reference). An example implementation of the bit circulation according to the present invention is described below. Alternative frequency rotations may be used for frequency interleaver design (an example frequency rotation is described in S. A. Mujtaba, “TGn Sync Proposal Technical Specification,” a contribution to IEEE 802.11, 11-04/0889r4, March 2005, incorporated herein by reference). Other bit circulation rules can also be applied. Although a certain bit may end up in an antenna different from its original one before bit circulation, similar system performance can be obtained as long as a certain bit is on the same position of the data groups before a splitting unit As such, the bit circulator In case of non-equal Mi, the splitter can split the output bits of the corresponding frequency interleaver into N The present invention has been described in considerable detail with reference to certain preferred versions thereof; however, other versions are possible. Therefore, the spirit and scope of the appended claims should not be limited to the description of the preferred versions contained herein. Referenced by
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